Jupiter's Io Generates Power and Noise, But No Magnetic Field

A great roar of acoustic waves near the north and south
poles of Jupiter's moon Io shouts about the power of the
volcanic moon.

The wave data, new pictures and other information
collected recently by NASA's Galileo spacecraft provide
insight into what happens above Io's surface, at its colorful
volcanoes and inside its hot belly. Scientists presented the
findings Monday at a meeting of the American Geophysical Union
in San Francisco.

Galileo, managed by NASA's Jet Propulsion Laboratory,
Pasadena, Calif., has been orbiting Jupiter for six years. As
it flew near Io's poles in August and October, the density of
charged particles it was passing through suddenly increased
about tenfold when the spacecraft crossed the path of a
magnetic-field connection between Io and Jupiter, reported Dr.
Donald Gurnett of the University of Iowa, Iowa City. The
waves, indicating the density, travel in a plasma of charged
particles, and would be silent to the ear, but Iowa
researchers converted them to sound waves to make the patterns
audible. Audio clips are available online at
http://www.jpl.nasa.gov/videos/io .

"You hear a whistling sound from Jupiter's radio
emissions, then, just when you go over the pole, you hear a
tremendous roar that starts abruptly, then stops abruptly,"
Gurnett said. "It's like the noise from a huge electrical
power generator." Io actually generates as much wattage as
about 1,000 nuclear power plants.

The region of increased density is where electrons and
ions come up from Io's tenuous atmosphere and follow a "flux
tube" where field lines from Jupiter's strong magnetic field
intersect Io. In a 1999 flyby of Io, Galileo had provided some
indication of the higher density over the moon's poles. This
year's two Io flybys were the first to show that those denser
areas coincide with the magnetic-field flux tube, Gurnett
said.

Recent magnetic-field measurements tell us something new
about the plumes erupting from Io's volcanoes and about the
moon's molten core, said Dr. Margaret Kivelson of the
University of California, Los Angeles.

"If this is the mechanism that's producing the currents,
it may help us in the search for active plumes," she said.

Galileo's routes near Io's north pole in August and near
its south pole in October were chosen for gaining measurements
to determine whether Io generates an intrinsic magnetic field
of its own within the greater magnetic field generated by
Jupiter.

"There's no intrinsic field," Kivelson said. "We can put
that question to rest." That means Io's molten iron core does
not have the same type of convective overturning by which
Earth's molten core generates Earth's magnetic field. Lack of
that overturning fits a model of Io's core being heated from
the outside, by tidal flexing of the layers around it, rather
than being heated from the center.

The heat generated inside Io by the tidal tug of Jupiter
makes this moon the most volcanically active world in the
solar system. A new color picture of one large volcanic
crater, Tupan Patera, shows various red, green, yellow and
black surface materials laid down by volcanic interactions of
molten rock and sulfur compounds, said Dr. Elizabeth Turtle of
the University of Arizona, Tucson. Tupan, named for a
Brazilian god of thunder, is one of Io's most persistent
volcanoes. Another new image reveals roofed-over portions of a
long lava channel, indicating that insulation provided by the
cover helped lengthen a large lava flow.

New infrared imagery from Galileo shows that darker areas
at Tupan correspond to hotter surface materials, said Dr.
Rosaly Lopes of JPL. The infrared data also confirm sulfur-
dioxide deposits near the source of a tall plume seen in
August above a previously inactive volcano.